Virtual substrates of the type discussed herein are substantially lattice matched layers of III-N semiconductor material, such as GaN, on a silicon substrate (wafer or portion thereof). A key component of this design is to maintain single crystallinity from the substrate to the top of the semiconductor layer. However, it is difficult to grow sufficiently thick layers of III-N directly on silicon because of the dislocations that propagate through the III-N. The growth of III-N on silicon, and in some applications other material such as rare earth oxides, involves the formation of compressive stress into the III-N layer during growth and the compressive stress results in dislocations rather than fractures as in tensile stress.
One prior art method of reducing dislocations in the GaN layer is to treat the GaN with SiH4 during growth. The mechanism for dislocation reduction is the formation of pits by SiH4 etching and overgrowing the pits with GaN. Dislocations in this case change direction and start growing horizontally instead of growing vertically (i.e. parallel to the c-axis).
Various methods have been proposed that incorporate several layers of crystal matching materials between the silicon substrate and the III-N semiconductor layers. One problem with these methods is that each additional layer increases the ultimate cost of the final product. It is desirable, therefore, to grow a III-N semiconductor layer directly on a silicon substrate or rare earth oxide material.
It would be highly advantageous, therefore, to remedy the foregoing and other deficiencies inherent in the prior art.
Accordingly, it is an object of the present invention to provide a new and improved method utilizing quantum dots for dislocation engineering of III-N.
It is another object of the present invention to provide a new and improved method utilizing quantum dots for dislocation engineering of III-N on silicon.
It is another object of the present invention to provide a new and improved virtual substrate structure including III-N grown directly on silicon with reduced dislocation density.
It is another object of the present invention to provide a new and improved virtual substrate structure of III-N grown directly on silicon and including alternating layers of Ge clusters or quantum dots and layers of III-N continued until dislocations in the III-N adjacent the upper surface are substantially eliminated.